September 25, 2020 Marlene H. Dortch, Esq. Secretary Federal Communications Commission 445 12th Street SW Washington DC 20554 Re: MB Docket No. 19-311 Dear Ms. Dortch: To supplement the record in the Commission’s proceeding to allow AM radio stations to voluntarily broadcast in the MA3 all-digital mode of HD radio, the National Association of Broadcasters (NAB) respectfully submits the attached summary of field test results of the HD Radio all-digital AM signal at nine stations, obtained by NAB as of 2015: NAB Labs All- digital AM Test Project, David H. Layer, National Association of Broadcasters, Washington, DC (2015 NAB BEC Proceedings) (also referred to as “Part I, NAB Labs All-digital AM Test Project”). We appreciate the opportunity to help inform the Commission’s consideration of this proceeding. Respectfully submitted, Larry Walke Associate General Counsel Legal and Regulatory Affairs National Association of Broadcasters 1771 N Street NW Washington DC 20036 2800 Phone 202 429 5300 Advocacy Education Innovation www.nab.org NAB Labs All-digital AM Test Project David H. Layer National Association of Broadcasters Washington, DC Abstract – Since 2012, NAB Labs has been conducting a with the only exceptions being a few low-power portable number of field tests (and more recently, laboratory testing) models (that are also FM-only). of the HD Radio all-digital AM signal.1 The purpose of this Further, within the broadcasting industry there has been test project has been to characterize the digital coverage more interest in the all-digital version of the AM system than performance and interference behavior of the all-digital AM the all-digital version of the FM system because, for a variety signal under a variety of conditions, with the goals of better of reasons, the hybrid AM system has not been widely understanding the capabilities and limitations of this signal deployed by broadcasters and has not received the same level and to develop a technical record in examining the feasibility of market acceptance as has the hybrid FM system. As a of possible FCC authorization of an all-digital AM service. result, some AM broadcasters have been looking beyond This paper provides a brief description of the all-digital AM hybrid to the all-digital AM system as a possible digital radio signal, then offers a summary of some of the field test results solution for the AM band. on nine stations obtained by NAB Labs to-date, as well as a Other than the technical information on the design of the discussion of the lab tests being conducted, and discusses all-digital AM system included in NRSC-5, there is little possible future test activities. information in the public record on the performance and capabilities of this system.3 The purpose of the test project Introduction reported on herein has been to add to this record by AM and FM band digital radio broadcasting in the United characterizing the digital coverage performance and States was authorized by the FCC in 2002, using the hybrid interference behavior of the system under a variety of mode of the HD Radio™ in-band/on-channel (IBOC) system conditions, with the goals of better understanding the developed by iBiquity Digital Corporation. [1] This digital capabilities and limitations of this signal and to develop a radio technology, standardized by the National Radio technical record examining the feasibility of possible FCC Systems Committee (NRSC) in 2005 as NRSC-5,2 supports authorization of an all-digital AM service. not only the hybrid mode of operation currently authorized for use (which includes both legacy analog and digital signal The HD Radio All-digital AM Signal components) but also an “all-digital” mode (not currently authorized) that eliminates the analog portion of the signal The all-digital AM signal consists of an unmodulated carrier and provides a number of benefits including improved which is surrounded by groups of orthogonal frequency robustness, a reduction in adjacent-channel interference, and division multiplexed (OFDM) digital subcarriers as shown in a greater coverage area than the hybrid version of the system. Figure 1. Some of the parameters of this signal are given in [2] Table 1. This signal is referred to as the “MA3” service mode, At the end of 2014, nearly 25 million HD Radio receivers and is presently designed to support a single audio channel were in the marketplace and nearly 2000 radio stations were (called the “main program service” or MPS) as well as broadcasting an HD Radio signal. [3] As marketplace supplementary data information (specifically, “program acceptance of this technology continues to increase, at some service data” or PSD and “station information service” or point broadcasters may consider introduction of the all-digital SIS).4 mode of operation. It has been generally accepted that an all- Part of the MA3 mode system specification includes an digital mode would not be introduced until market penetration RF mask which constrains the spectral emissions.5 This mask of receivers was sufficiently high, since once broadcasters was designed based on a theoretical analysis of the MA3 switch to all-digital operation, analog radio receivers (those mode of operation so as to minimize the impact of out-of-band not equipped to receiver the HD Radio signal) will go silent. (i.e., beyond the ±10 kHz full bandwidth spectrum of the Note that the vast majority of HD Radio receivers being sold signal) emissions on adjacent-channel signals while are capable of receiving both hybrid and all-digital signals, 1 Created in 2012, NAB Labs is an initiative of the National Association of 3 Limited field tests were conducted by iBiquity in 2002 at stations WTOP- Broadcasters (NAB), providing a platform for innovation, a venue for AM in Washington, DC and WD2XAM in Cincinnati, OH and reported on forging partnerships and testing new technology, and educational events to in [4]. The next engineering report on this system was not published until create awareness about over-the-air radio and television technology 2013, as part of the project being discussed in this paper. [5] initiatives. 4 Note that the hybrid AM signal is referred to as the “MA1” service mode. 2 Since its original adoption, the NRSC-5 Standard has been updated by the 5 See [7], Section 4.5.4. NRSC three times, most recently in 2011 (NRSC-5-C). 2015 NAB BEC Proceedings — 19 reached where the secondary and tertiary digital sidebands will not have sufficient signal strength to be decoded and the receiver will at that point “blend” from enhanced audio to core audio. Continuing away from the transmitter, there will then come a point where the primary digital sidebands are too weak (or too heavily interfered with) to be decoded and at that point the receiver will either mute or static will be heard corresponding to the noise and/or co-channel signal energy present.8 Throughout this paper, this point will be referred to as the all-digital AM point-of-failure or simply POF. This is in contrast to the operation of the hybrid AM system which has an analog AM signal component to which the receiver “blends” when the (hybrid) digital signal components can no Figure 1. All-digital AM signal spectrum - from [6], Figure 5-4 longer be received. simultaneously attempting to not overly constrain the signal. It should be noted that the greatest extent of coverage of As will be discussed below, in implementing this signal at the MA3 mode is determined by the coverage of the primary nine different radio stations as part of the field test portion of digital sideband components of the signal, and that the this project, currently available transmission equipment had coverage of the core audio service will be the same whether some difficulty in meeting the RF mask as specified in [7]. the system is operated in full bandwidth or reduced bandwidth mode. The co- and adjacent-channel interference behavior of Table 1. All-digital AM system parameters the full and reduced bandwidth modes will be different, of course, as will the RF mask compliance (since the more VALUE broadband full bandwidth signal will generate greater out-of- REDUCED BW FULL BW band emissions than will the reduced bandwidth signal).9 PARAMETER CONFIG. CONFIG. RF bandwidth ±5 kHz ±10 kHz Channel Field testing of the All-digital AM Signal 20 kbps 40 kbps information rate ≈ 104 (54 from core Early field testing of the HD Radio AM system in all-digital Digital subcarriers ≈ 54 plus 50 additional) mode was reported by iBiquity in April 2002. [4] Testing was Main channel Mono or conducted at two stations: WTOP-AM (1500 kHz, Two-channel stereo audio parametric stereo Washington, DC, class A, 50 kW, nighttime only), and % of signal power WD2XAM (1660 kHz, Cincinnati, OH, class D, 10 kW, in unmodulated 37% 36% daytime only). For these early tests, the unmodulated carrier carrier6 power was set to 50% of the total signal power which is higher Station information service (SIS), Data broadcasting Program service data (PSD), Emergency than the level presently specified for the system (refer to Table capabilities alert system (EAS) 1). The genesis of the field testing being reported on in this A broadcaster may transmit either the full bandwidth or the paper stems from when NAB Labs was approached by CBS reduced bandwidth signal. The reduced bandwidth signal Radio in 2012, offering to make AM station WBCN (1660 consists of just the unmodulated carrier and the primary kHz, Charlotte, NC) available on a limited basis for all-digital digital sidebands (shown in Figure 1) while the full bandwidth AM testing, and providing an opportunity to begin developing signal includes the secondary and tertiary digital sidebands, a contemporary test record that would help educate the as well.7 Note that the audio signal received using all three industry as to the capabilities of all-digital operation, develop digital sideband groups is considered “enhanced” audio, all-digital operational parameters, and provide information while the audio signal derived from just the primary digital which could be eventually submitted to the FCC for the sidebands is considered “core” audio.